1. The Field of the Invention
The present invention relates generally to the packaging of photonic devices, such as lasers or detectors. More particularly, the present invention relates to aligning a lens of a cap and a photonic device of a photonic device package.
2. The Relevant Technology
Referring to FIG. 1, a common package design 100 for a photonic device 104, such as a laser, includes a header 102, such as a TO header, and a cap 112 with a flat window 114 for coupling light between package 100 and at least one other optical element, such as an optical fiber. Header 102 typically includes pins 106 for feeding electrical signals through appropriate insulating feedthroughs, such as a glass or ceramic region. Header 102 typically includes a region 108 for mounting photonic device 104, sometimes known as a “stem”. For example, if photonic device 104 is an edge-emitting laser, the laser is mounted onto the stem using a laser submount. The header includes a baseplate 110 having a comparatively flat annular region that forms a seating surface for bonding a lip region 116 of cap 112 to header 102.
In some applications it is desirable to replace flat window 114 of cap 112 with a micro-lens. The micro-lens can be selected to improve the optical coupling of photonic device 104 in package 100 with an exterior optical element. For example, if photonic device 104 in package 100 is a laser, a micro-lens can be integrated in cap 112 to improve the optical coupling of the laser to an optical fiber, optical waveguide, or other optical device used to transmit the optical signal generated by the laser.
Incorporating a lens into cap 112 has the drawbacks that the packaging cost tends to increase and that the laser yield tends to decrease. Header 102 and cap 112 are typically formed using a manufacturing process with comparatively poor mechanical tolerances compared with optical dimensions. Consequently, an active alignment process is required to align the cap to the laser prior to a hermetic sealing process. In an active alignment process, the output of package 100 is optimized with the photonic device in an active state. For example, if the photonic device is a laser, the light output of the laser is monitored outside of the package (e.g., using an optical detector) and the cap is positioned with actuators until the output of the laser is optimized.
However, active alignment techniques have several drawbacks. First, active alignment is more expensive than desired, in part due to the numerous measurements required to determine an optimum cap position. Additionally, the mechanical apparatus to position and hold the cap in place during final sealing requires accurate alignment actuators that increase the cost of the system. Moreover, slippage can occur after alignment during final sealing of the cap, resulting in reduced yield.